This invention relates generally to acoustic transducers and in particular to electro-acoustic transducers in the low frequency range.
The basic principle of the present invention is disclosed in applicant's prior U.S. Pat. No. 3,636,278, issued Jan. 18, 1972.
The present invention represents an improvement on the basic concept and a specific configuration and method of construction for such a sound reproduction device in the low frequency range from about 0 to 5000 Hz. Coverage of this range might also be accomplished using two electro-acoustic transducers using the concept of the present invention with one dimensioned to produce sound in the 0- 500 Hz range and the other to produce sound in the 500-5000 Hz range.
Prior to the invention of the electro-acoustic transducer disclosed and claimed in applicant's prior issued patent, the majority of transducers used to produce sound in the low frequency range utilized light weight cones driven by a coil attached to a cylinder suspended in a magnetic field.
In such devices, and for that matter in any vibrating diaphragm driven by a motion inducing force located at one point or at a small area on the diaphragm, all parts of the diaphragm will not be moving in the same direction with the same velocity for the same distance or at the same time due to the flexibility of the diaphragm material as well as the assymetric forces at the point of attachment of the diaphragm to the surrounding frame and the inertial forces of the air against the diaphragm.
The prior art methods used to correct the above problems usually resulted in a configuration of foam plastic filled cones in which the base of the cone was used as the air driving surface and the apex of the cone as the point of application of the motion inducing force. Such a configuration generally required large driving forces to overcome the inertial forces of the large mass of the foam filled cone.